The present invention relates to gaseous discharge devices, such as those used to create luminous displays or signs; and particularly to the power supply for exciting a gaseous discharge device.
Luminous displays are constructed by infusing a gas, such as neon or argon, into a hermetically sealed transparent structure, such as a tube or a sandwich of plates. When a high alternating excitation voltage is directly or indirectly applied to the gas, the gas ionizes causing it to glow.
The conventional power supply for applying the excitation voltage to the gaseous discharge device comprised merely a high voltage transformer which stepped the line voltage (120 volts at 60 Hertz or 240 volts at 50 Hertz) up to the high excitation voltage. Although this power supply is simple, it is relatively bulky and heavy. When the transformer is integrated with a gaseous discharge device, packaging must be provided to insure that the heavy transformer does not come into contact with the device during shipment to avoid damage. In addition, different transformers must be provided if the discharge device is to be supplied with 120 volts or 240 volts.
An alternative type of high voltage power supply is commonly referred to as a resonant converter. In this device, the primary winding of the transformer was connected to a resonant circuit which applied pulses of the rectified line voltage to the primary winding, as described in U.S. Pat. No. 4,613,934. Because of the resonant nature of the supply circuit, the peak voltage applied to the primary winding was several times the supply line voltage and the frequency of the primary voltage is several hundred times the supply line frequency. This enabled the number of windings of the primary to be reduced, and the transformer core made lighter. A transistor often was used to switch the current to the primary winding and care had to be taken that the transistor was switched off only when the resonating current went to zero else the transistor might fail.
Another drawback to gaseous discharge devices in general is the difficulty encountered when one wants to create flashing illumination. Very sophisticated power supply circuits are required to produce an intermittent excitation of the gaseous discharge device, since switching of a control transistor at random times during the excitation cycle can cause the transistor to fail.